This invention relates in general to apparatus for working on sheet material and deals more particularly with an improved machine for progressively working on a long lengths of sheet material wound on tubular roll cores and wherein the machine includes at least one hub assembly for driving and/or supporting a roll core to pay-off and/or take-up sheet material processed by the apparatus.
In a machine of the type with which the present invention is concerned, such as a plotter, for example, work is progressively performed on successive sections of an elongated web of sheet material supported on a work surface. A tool such as a plotting instrument or pen supported for movement in at least X and Y coordinate directions relative to the work surface in response to command signals received from a programmable controller performs the work. The machine may operate intermittently alternately advancing the sheet material relative to the work surface and performing work on the sheet material after the sheet material has been advanced and while it is maintained in a stationary position relative to the work surface or the machine may operate continuously, simultaneously advancing the sheet material and working on the material as it is advancing across the work surface.
If the sheet material processed by the machine is to be stored for later use or moved to another machine for further processing the present machine may include both a pay-off or supply roll and a take-up roll. However, if material processed by the machine is to be separated from the web at the machine for immediate use the machine may include only a supply roll. In either instance it is essential to precisely control the positioning and movement of the web material relative to the work surface to coordinate the position of the material relative to the tool to assure a satisfactory work product.
Such a machine must, of course, be adapted to process commercially available rolls of sheet material. Such rolls generally comprise sheet material wound on cylindrical tubular cardboard roll cores. Hub assemblies are usually employed to support the rolls of material and interface with the motor or motors which rotate the rolls. Roll dimensional consistency has proven critical to providing proper interface, but, unfortunately, core dimensions are not always consistent, especially where the material is obtained from more than one manufacturer or imported from more than one country.
Roll cores often vary in thickness and both in outside and inside diameter. Although the axial length of a roll core and the width of the material wound thereon are usually equal, the ends of the roll core are not always flush with the radially disposed ends of the wound material. Thus, for example, a roll core may extend from one end of a roll of wound material and be recessed with respect to the opposite end of the wound roll. These dimensional inconsistencies and winding irregularities present problems in providing proper hub interface.
A typical hub assembly includes a hub for coaxial positioning within the end of an associated roll core and a radially disposed annular flange for engagement or near engagement with an associated end of the roll core and an associated radially disposed end face of the sheet material wound thereon. If the roll core protrudes from one end of the wound sheet material and is recessed with respect to the opposite end of the material the flange on the end from which the core protrudes will be spaced from the end face of the wound sheet material. As the sheet material is paid-off of such a roll, the material spaced from the flange will have a tendency to telescope so that material will leave the roll traveling in a skewed path relative to the roll axis as the roll of material rotates. If the inside diameter of the roll core is too small difficulty will be encountered in assembling a hub with and removing a hub from the roll core. If the inside diameter of the roll core is too large the drive hub will not transfer rotation of the drive motor to the roll of material.
Accordingly, it is the general aim of the present invention to provide an improved machine of the aforedescribed general type which includes a hub assembly for supporting and/or driving a roll of sheet material having a generally cylindrical tubular cardboard roll core and wherein the hub assembly compensates for inconsistencies in the dimensioning of the roll core and irregularities in the manner in which sheet material is wound onto the core to assure proper tracking of the sheet material as it leaves the roll and passes through the machine.